No it will not flood proof it. It (the Durock) will withstand water for sure, but the plaster or any other interior finish will not stand up to flooding. There is really nothing you can do to prevent problems with flooding other than moving yourself or your house to higher ground. Also you will have problems with water getting behind the walls and molding as well. I feel for you, and know you would really like a solution to your problem as your house now sits but the reality is there is no solution where you are located. I'm glad to be on higher ground here in Apopka for sure.